Localization and coherent control of 25 nuclear spins in Silicon Carbide

TL;DR

The paper addresses the challenge of characterizing and coherently controlling a large nuclear-spin environment surrounding a solid-state defect to enable scalable quantum registers. It combines high-fidelity SSR readout with DDRF and SEDOR-based correlation spectroscopy to map, address, and chain nuclear spins, and reconstructs 3D positions via an iterative lattice-based localization refined by least-squares fitting. The authors localize a cluster of 25 nuclear spins around a single V2 center in 4H-SiC, map hyperfine and inter-nuclear couplings, and validate these parameters against density functional theory predictions, establishing a complete local-register workflow in SiC. This work demonstrates the viability of SiC color centers as robust nodes for quantum networks, memories, and distributed quantum information processing using tightly integrated local nuclear-spin registers.

Abstract

Optically addressable spin defects are excellent candidate platform for quantum sensing and quantum network. Nuclear spins coupled to color centers naturally enable long lived quantum memories and local qubits registers. To fully leverage this potential precise characterization of the surrounding nuclear-spin environment augmented with refined DFT models is required. In this work, we report angstrom-level 3D localization of 25 nuclear spins around a single V2 center in 4H Silicon Carbide. Utilizing specially placed robust nuclear memory as a highly efficient readout ancilla for readout, we apply correlation based spectroscopy and by selecting multi-spin chains up to length four, we access and characterize extended nuclear spin cluster. Using the coupling map we reconstruct their couplings to the central electron spin and neighboring nuclei. This work paves the way towards advanced quantum register applications on Silicon Carbide platform.

Figures (5)

• Figure 1: a) Schematic of V2 defect surrounded by $^{29}$Si and ${^13}$C isotopes. b) Single shot readout of Si1 nuclear spin qubit c) Electron and nuclear spin coherence $T_2$ and electron spin-lattice relaxation $T_1$ time.
• Figure 2: a) Quantum circuit representation and pulse-train diagram of the DDRF gate. b) Scan of the silicon bath. Multiple distinct lines indicate possible control over several nuclear spins. Si3 and Si4 resonances are from the $m_s=-1/2$ subspace. Two Si12 resonances can be seen due to two different electron subspaces. All other marked resonances belong to $m_s=3/2$. c) Scan of the carbon bath. Two resonances, according to two electron states are visible. d) Quantum circuit diagram for initialization, manipulation and readout of a nuclear spin via DDRF. e) Amplitude calibration of the DDRF gate. The dashed line indicates the amplitude which rotates the nuclear spin onto the equator of the Bloch sphere, resulting in an effective CNOT gate. f) Rabi oscillation of Si4. Recorded by the sequence depicted in d.
• Figure 3: a) SEDOR measurement with Si1 being the probe spin. 14 silicion and 2 carbon spins can be observed. The contrast of each peak in the spectrum depends on the individual coupling between probe and target. Spins with small A$_\parallel$ typically are distant from Si1, thus a increased interaction time of $\tau$ is applied. The linewidth is inverse proportional to the $\pi$-pulse duration. Inset: Si1 is used as a probe to sense surrounding isotopes. b) Quantum circuit of a SEDOR measurent. The probe is initialisd either via SSR (Si1) or via DDRF (all others). c) Scan of the interaction time $\tau$ at a fixed target frequency.
• Figure 4: a) Graph representation of the 27-spin network. Each circle represents an isotope (green for silicon, orange for carbon). Grey lines indicate the extracted oscillation frequencies obtained via SEDOR. Couplings below 1 Hz are omitted for clarity. The highlighted links denote the spin chains analyzed in panel b. b) Spin chains. c) Pulse train diagram of nested correlation measurements. d) Experimentally observed oscillation frequencies $f_{ij}$. The spins are arranged such that the emerging clusters (highlighted by blue squares) are grouped. The couplings within each square are used to reconstruct the internal structure of the corresponding cluster, while the couplings outside the squares provide information about the relative spatial arrangement of the clusters with respect to one another.
• Figure 5: a) Starting from spin A, multiple position candidates for spin B and C are marked based on $C_{AB}$ and $C_{AC}$. b) Including $C_{BC}$ eliminates two marked positions of spin C. c) Spin D shows strong coupling to C. This allows only single positions of D relative to C. d) Based on $C_{AD}$ and $C_{BD}$ two positions of D can be ruled out. e) Spin positions of 25 nuclear spins around central electron spin found by an iterative placement algorithm. Couplings below 2 Hz are omitted for clarity